The objectives of the work described in this application are to further our understanding of neuronal organization in visual cortex and examine the molecular mechanisms that underlie the processing of visual information. Anatomical methods have been used to describe cortical structure, the types of neurons and their projections and examine the neurotransmitter that they use, but the post-synaptic aspects of neuronal communication in visual cortex has not been studied extensively. Several different post-synaptic receptors have been identified for many of the cortical neurotransmitters. Furthermore, these receptor sub-types mediate different responses in the post-synaptic neuron. Therefore, it is important, when ascribing a role in cortical processing to a group of neurons, to know not only the anatomy of the nerve fibres containing the neurotransmitter, but also the nature of the post-synaptic receptor on which it is acting. In this proposal, neurotransmitter receptors in visual cortex will be examined by radioligand binding techniques. The neurotransmitter receptors of interest will include those for norepinephrine, dopamine, 5-hydroxytryptamine, GABA, and acetylcholine. The receptor subtypes for each of these neurotransmitters will be investigated and their pharmacological properties determined. The location of these receptors and their subtypes will be demonstrated on tissue sections that have been labeled with ligands that bind to specific receptor sites and then visualized by autoradiography. These studies will be performed on visual cortex of cat, macaque and human (post-mortem tissue). The results of these investigations will, when correlated with existing knowledge of the physiology and anatomy of cat and macaque visual cortex, allow a more comprehensive understanding of cortical structure and function.